A wealth of evidence suggests that the immune system, specifically T cells, can recognize and destroy malignant cells. However, despite adequate priming of tumor-specific T cells, tumor regression has rarely occurred in vaccine or adoptive cell therapy trials to date. These observations suggest that immune suppressive mechanisms in the tumor microenvironment may dominate and allow tumor escape. Research suggests that when such mechanisms are reversed, improved anti-tumor responses can occur. In a murine adoptive immunotherapy model, Dr. Kline has pursued strategies to reverse two putative inhibitory mechanisms: T cell anergy and regulatory T cells. He has found that T cell anergy can be reversed through the process of lymphopenia-induced homeostatic proliferation and that regulatory T cells can be removed prior to the adoptive transfer of bulk T cells into lymphopenic hosts. When homeostatic proliferation is combined with regulatory T cell depletion, potent tumor rejection occurs. These results have prompted Dr. Kline to develop a phase I protocol to test the effectiveness of this strategy in cancer patients. During the proposed award period, Dr. Kline proposes to investigate the effectiveness of total body irradiation in inducing lymphopenia in cancer patients, and to determine whether homeostatic proliferation of autologous polyclonal T cells depleted of regulatory T cells occurs following transfer into such irradiated hosts. Analysis of safety, in particular focusing on autoimmunity, will be pursued. An additional goal is to determine if this approach is associated with objective tumor responses. This research, if successful, could serve as a platform for future clinical trials and may have a significant impact on the way in which novel cancer immunotherapeutic strategies are developed and delivered. Lastly, a continued exploration of other inhibitory tumor escape mechanisms will ensue in the laboratory setting. Overall, this research may generate significant findings with important ramifications to public health, as it may offer a new approach to the treatment of patients with advance malignant diseases, who otherwise have a limited number of therapeutic options, and a universally poor outcome. Enhancing on his early training in both clinical and basic scientific research, Dr. Kline expects to build the necessary expertise required for a career in translational cancer immunotherapy research.